1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer, an image forming method and storage medium therefor.
2. Description of the Related Art
An image forming apparatus such as a laser printer includes a photosensitive drum on which electrostatic latent images are formed based on image data, a developing roller for developing the electrostatic latent images formed on the photosensitive drum into toner images, a transfer roller to which a transfer bias having a reverse polarity to the photosensitive drum is applied, and the like. The photosensitive drum and the developing roller are disposed facing each other, and are rotatably driven in predetermined directions, respectively. The developing roller holds a toner that is charged in the same polarity as the photosensitive drum. The electrostatic latent image formed on the surface of the photosensitive drum is developed into a toner image by the toner supplied from the developing roller when it faces the developing roller. Thereafter, the toner image is transferred to a sheet of paper conveyed between the photosensitive drum and a transfer roller, which is disposed facing the photosensitive drum, when the toner image faces the transfer roller.
In the image forming apparatuses thus structured, the so-called cleanerless type image forming apparatus is known in which the residual toner on the photosensitive drum after the transfer of the toner image is collected by the developing roller. Since the cleanerless type image forming apparatus does not need a cleaner device such as a blade or a reserving unit for a discarded toner, the device structure can be simplified and miniaturized, and the cost can be reduced.
However, in a cleanerless type image forming apparatus, paper dust generated from the paper that is attached to the photosensitive drum may cause a defective image forming (hereinafter, referred to as “printing of paper dust”). In other words, the paper dust attached to the photosensitive drum is charged to the same polarity as the photosensitive drum (same polarity as the toner) when the photosensitive drum is uniformly charged by a charger, thereafter, however, the paper dust is charged to the reverse polarity by being rubbed strongly with the toner held by the developing roller when it faces the developing roller. Then, the toner sticks to the paper dust, and the paper dust attached to the toner ends up being transferred to the sheet of paper.
Therefore, it has been proposed that the circumferential speed of the developing roller (moving speed of the surface of the developing roller) is set to 1.1 to 1.25 times the circumferential speed of the photosensitive drum (moving speed of the surface of the photosensitive drum) so that, even when paper dust is attached to the photosensitive drum, the paper dust is not strongly rubbed against the toner held by the developing roller, thereby preventing the occurrence of the printing of paper dust (for example, refer to JP-A-2001-356590).